A resist obtained from an alkyladamantyl ester used as a raw material has been reported to have high dry etching resistance in a production process of a semiconductor (JP-A 5-265212), and the possibility of its use as a material for a resist for a semiconductor has been coming into notice.
In general, a compound used as a material for a resist for a semiconductor is required to be of high purity. Even in the case of the above alkyladamantyl ester, it is required to be of high purity when used as a material for a resist for a semiconductor. Particularly, the alkyladamantyl ester is stringently required to have a metal component reduced. Further, as a purification method capable of removing such a metal component efficiently, purification by distillation is suitable.
It is known that the alkyladamantyl ester is generally unstable with acids and is decomposed into an alkylidene adamantane and a carboxylic acid by a catalytic amount of acid. Therefore, it has been generally practiced that the alkyladamantyl ester is washed with an alkali aqueous solution such as a sodium hydroxide aqueous solution as a pretreatment when the alkyladamantyl ester is purified by distillation.
However, as a result of attempting to distill the alkyladamantyl ester by such a method, the present inventors have found that the alkyladamantyl ester decomposes easily during distillation depending on a synthesis method of the alkyladamantyl ester. That is, it has been found that an alkyladamantyl ester synthesized by alkylating 2-adamantanone with an organic metal reagent and then causing an acid halide to react with the resulting product decomposes during distillation and causes a blockage in a distillation device by sticking to the internal wall of the device, whereby purification by distillation may become substantially impossible.
The present inventors have made intensive studies so as to solve the above problem. As a result, they have found that an alkyladamantyl halide (hereinafter also referred to as “impurity halide”) represented by the following formula (2):
(wherein R2 is an alkyl group having 1 to 6 carbon atoms, and X is a halogen atom)    is contained in an alkyladamantyl ester produced by such a method as described above, that the impurity halide is hardly removed by a conventional alkaline treatment using an alkaline aqueous solution in a heterogeneous system, that the impurity halide thermally decomposes at the time of distillation and produces a hydrogen halide which acts as a catalyst and decomposes a target alkyladamantyl ester. Under the circumstances, as a result of further studying a method of removing the impurity halide, the present inventors have found that although the impurity halide could not be removed efficiently and completely by a silica gel treatment or an activated carbon treatment, it can be removed efficiently by carrying out an alkaline treatment in a homogeneous system.
Further, the present inventors have also found in these studies that when the alkyladamantyl ester contains the above impurity halide in large quantity, there occur such problems that the alkyladamantyl ester decomposes and causes coloration and the like during storage or transportation and that a molecular weight does not increase at the time of polymerization.